The homeland of Osama bin Laden's father, Yemen has long been a top U.S. security concern. For years, al Qaeda militants -- including at least one Saudi released from U.S. custody in Guantanamo Bay, Cuba -- have taken refuge here. One complication surrounding the closing of the U.S. military prison at Guantanamo is what to do with the nearly 100 Yemeni detainees there. U.S. intelligence officials say they have little confidence in the Yemeni government's ability to keep them in prison back in their home country.

Since the 2000 al Qaeda attack on the USS Cole in the Yemeni port of Aden, U.S. officials have reported mixed results from the Yemeni government in the fight against terrorism. President Ali Abdullah Saleh established a rehabilitation program for jailed Islamic militants, but hasn't curbed the growing network of al Qaeda fighters who have flocked to lawless parts of Yemen and are using the country as a launching pad for attacks.

The new offensive comes as al Qaeda in the Arab Peninsula, as the local branch of the militant group is called, appears to be gaining strength. An Arab intelligence official says that al Qaeda fighters fled to Yemen this summer from Pakistan and Afghanistan, where the movement has suffered military setbacks in recent months.

While the number of fighters retreating to Yemen is unknown, the movement is worrying Yemen's Arab and African neighbors. Recently, al Qaeda announced the merging of the Saudi and Yemeni branches of the organization in Yemen after a crackdown by Saudi authorities.

A Saudi militant, traveling from an al Qaeda safe house in Yemen, injured Saudi Arabia's deputy interior minister in a failed suicide-bombing attack last month.

In 2008, al Qaeda in the Arabian Peninsula claimed responsibility for two suicide-bomb attacks against the U.S. Embassy in Sana'a, the Yemeni capital, in which 16 Yemenis were killed. This year, the group claimed responsibility for an attack that killed four Korean tourists and two of their Yemeni security guards.

Al Qaeda operatives in Yemen are also aiding Islamic rebels trying to topple the Somali government, according to U.N. officials in Somalia and Yemen. Al Shabab, the Somali insurgency group that U.S. officials view as an al Qaeda proxy in East Africa, restocks with fighters and weapons through Yemeni smugglers working the narrow Red Sea passage between the two countries, these officials said.